Hydrogen-storage alloy

ABSTRACT

In a hydrogen-storage alloy which is a high-entropy alloy having a molecular formula of Co u Fe v Mn w Ti x V y Zr z , the hydrogen-storage alloy is an alloy free from rare-earth elements and having a stable single C14 Laves phase structure. The hydrogen-storage alloy has a high capacity of absorbing and releasing hydrogen under ambient temperature and pressure and a high hydrogen-storage capacity at room temperature, so that the hydrogen-storage alloy can be used extensively in the fields of hydrogen storage, heat storage, heat pump, hydrogen purification, isotope separation, secondary battery and fuel cell without producing harmful polluted gases, and the hydrogen-storage alloy has high potential for the development of a green energy source.

BACKGROUND OF THE INVENTION

1. Field of the invention

The present invention relates to a hydrogen-storage alloy system that contains no rare-earth elements, and, more particularly, to a hydrogen-storage alloy system with a stable alloy structure and a high capacity of absorbing and releasing hydrogen under ambient temperature and pressure.

2. Description of Related Art

Owing to energy crisis and harms done to the earth by the present ways of using energy sources, the development of green energy sources, including the usage of natural hydrogen energy, solar energy, bio-energy, geothermal energy, and tidal energy, in the most economic condition becomes a notable research and development subject, and any energy source and method causing no threats to the environmental pollution is studied extensively.

Hydrogen is a chemical element whose reserve ranks the third among all elements in the world. Heat can be produced in a quantity of 140 kJ per kg of hydrogen when hydrogen gas is combusted. In addition to the advantage of an excellent combustion rate, the product produced by the combustion is pollution-free water, and thus hydrogen has become a popular green energy source. Since Ni—H battery features a large storage capacity and a high stability, the Ni—H battery becomes very popular when it comes to the decision of choosing an energy source for applications in different areas, particularly in the research and development of hydrogen fuel cell cars. However, hydrogen is highly flammable, so that if hydrogen is used as energy for generating electric power, the storage of hydrogen becomes a safety issue. On the other hand, hydride features a low price, a high safety, an advantage of not producing green house gases, a high storage capacity, and a property of absorbing and releasing hydrogen easily, and thus hydride is considered as an excellent hydrogen storage material.

In recent years, high-entropy alloy (HEA) is one of the most noticeable materials and composed of at least five principal elements, and each element has an atomic percentage falling within a range of 5%˜35%. After the elements are mixed uniformly in a liquid phase at a high temperature and then cooled, a hydrogen storage alloy with the characteristics of high entropy and low Gibbs free energy is formed. Compared with a conventional alloy, the high-entropy alloy has a simpler microstructure that can be used to produce a nano-scaled material easily and features the advantages of high thermal stability, excellent ductility and compressibility, high hardness, and outstanding electric and magnetic properties. It is noteworthy to point out that the proportion of metal elements selected and mixed to form such an alloy material has a substantial effect of storing hydrogen, and absorbing/desorbing hydrogen of the alloy, and optimal conditions are applied for the usage of the alloy.

SUMMARY OF THE INVENTION

Therefore, it is a primary objective of the present invention to provide a hydrogen-storage alloy with an optimal hydrogen-storage performance to enhance the usage. The inventor of the present invention developed a hydrogen-storage alloy that uses a vacuum arc remelting (VAR) method and a thermal treatment, if necessary, to prepare an as-cast high-entropy alloy.

The hydrogen-storage alloys of the present invention have a molecular formula Co_(u)Fe_(v)Mn_(w)Ti_(x)V_(y)Zr_(z), where 0.5≦u≦2.0, 0.5≦v≦2.5, 0.5≦w≦2.0, 0.5≦x≦2.5, 0.4≦y≦3.0 and 0.4≦z≦3.0, and such hydrogen-storage alloys can be a non-equal molar alloy material with a structure of a single C14 Laves phase, and the structure is stable and capable of absorbing and desorbing hydrogen in an operation environment under ambient temperature and pressure and a high ratio of the weight percentage of the total number of hydrogen atoms to the weight percentage of the total number of alloy atoms (H/M value), which indicates a high hydrogen-storage capacity.

The hydrogen-storage alloys of the present invention can be used extensively in the areas of hydrogen storage, heat storage, heat pump, hydrogen purification, isotope separation, secondary battery and fuel cell.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, as well as its many advantages, may be further understood by the following detailed description and drawings in which:

FIG. 1 is a schematic view showing the distribution of all compositions of a hydrogen-storage alloy in accordance with the present invention;

FIG. 2A shows X-ray diffraction patterns of hydrogen-storage alloys with different titanium contents of the present invention before the test of a pressure-composition-isotherm curve takes place;

FIG. 2B shows X-ray diffraction patterns of hydrogen-storage alloys with different titanium contents of the present invention after the test of a pressure-composition-isotherm curve takes place;

FIG. 3 is a temperature versus titanium content graph of a hydrogen-storage alloy of the present invention showing the hydrogen absorption capacity of the hydrogen storage alloys with different titanium contents at different temperatures;

FIG. 4A is a pressure-composition-isotherm curve of hydrogen-storage alloys with different titanium contents at 25° C. in accordance with the present invention;

FIG. 4B is a pressure-composition-isotherm curve of hydrogen-storage alloys with different titanium contents at 80° C. in accordance with the present invention;

FIG. 5A shows X-ray diffraction patterns of hydrogen-storage alloys with different vanadium contents of the present invention before the test of a pressure-composition-isotherm curve takes place;

FIG. 5B shows X-ray diffraction patterns of hydrogen-storage alloys with different vanadium contents of the present invention after the test of a pressure-composition-isotherm curve takes place;

FIG. 6 is a temperature versus vanadium content graph of a hydrogen-storage alloy of the present invention showing the hydrogen absorption capability of the hydrogen storage alloy with different vanadium contents at different temperatures;

FIG. 7A shows X-ray diffraction patterns of hydrogen-storage alloys with different vanadium contents of the present invention before the test of a pressure-composition-isotherm curve takes place;

FIG. 7B shows X-ray diffraction patterns of hydrogen-storage alloys with different vanadium contents of the present invention after the test of a pressure-composition-isotherm curve takes place;

FIG. 8 is a temperature versus vanadium content graph of a hydrogen-storage alloy of the present invention showing the hydrogen absorption capacity of the hydrogen storage alloy with different vanadium contents at different temperatures;

FIG. 9A shows X-ray diffraction patterns of hydrogen-storage alloys with different manganese contents of the present invention before the test of a pressure-composition-isotherm curve takes place;

FIG. 9B shows X-ray diffraction patterns of hydrogen-storage alloys with different manganese contents of the present invention after the test of a pressure-composition-isotherm curve takes place;

FIG. 10 is a temperature versus manganese content graph of a hydrogen-storage alloy of the present invention showing the hydrogen absorption capacity of the hydrogen storage alloy with different manganese contents at different temperatures;

FIG. 11A shows X-ray diffraction patterns of hydrogen-storage alloys with different cobalt contents of the present invention before the test of a pressure-composition-isotherm curve takes place;

FIG. 11B shows X-ray diffraction patterns of hydrogen-storage alloys with different cobalt contents of the present invention after the test of a pressure-composition-isotherm curve takes place;

FIG. 12 is a temperature versus cobalt content graph of a hydrogen-storage alloy of the present invention showing the hydrogen absorption capacity of the hydrogen storage alloy with different cobalt contents at different temperatures;

FIG. 13A shows X-ray diffraction patterns of hydrogen-storage alloys with different iron contents of the present invention before the test of a pressure-composition-isotherm curve takes place;

FIG. 13B shows X-ray diffraction patterns of hydrogen-storage alloys with different iron contents of the present invention after the test of a pressure-composition-isotherm curve takes place;

FIG. 14 is a temperature versus iron content graph of a hydrogen-storage alloy of the present invention showing the hydrogen absorption capacity of the hydrogen storage alloy with different cobalt contents at different temperatures.

Description of Designations Used for Representing Respective Elements of the Present Invention: According to the design of experiment of the present invention, any alloy with a mole ratio of 1.0 is identical to each other. In other words, A2=B3=C3=D4=E4=F2. An alloy with an equal mole ratio correlates to an indicated alloy of the non-equal molar alloys having different metal contents in the system.

A1 is a high-entropy hydrogen-storage alloy containing titanium of 0.5 mole ratio.

A2 is a high-entropy hydrogen-storage alloy containing titanium of 1.0 mole ratio.

A3 is a high-entropy hydrogen-storage alloy containing titanium of 1.5 mole ratio.

A4 is a high-entropy hydrogen-storage alloy containing titanium of 2.0 mole ratio.

A5 is a high-entropy hydrogen-storage alloy containing titanium of 2.5 mole ratio.

B1 is a high-entropy hydrogen-storage alloy containing zircon of 0.4 mole ratio.

B2 is a high-entropy hydrogen-storage alloy containing zircon of 0.7 mole ratio.

B3 is a high-entropy hydrogen-storage alloy containing zircon of 1.0 mole ratio.

B4 is a high-entropy hydrogen-storage alloy containing zircon of 1.3 mole ratio.

B5 is a high-entropy hydrogen-storage alloy containing zircon of 1.7 mole ratio.

B6 is a high-entropy hydrogen-storage alloy containing zircon of 2.0 mole ratio.

B7 is a high-entropy hydrogen-storage alloy containing zircon of 2.3 mole ratio.

B8 is a high-entropy hydrogen-storage alloy containing zircon of 2.6 mole ratio.

B9 is a high-entropy hydrogen-storage alloy containing zircon of 3.0 mole ratio.

C1 is a high-entropy hydrogen-storage alloy containing vanadium of 0.4 mole ratio.

C2 is a high-entropy hydrogen-storage alloy containing vanadium of 0.7 mole ratio.

C3 is a high-entropy hydrogen-storage alloy containing vanadium of 1.0 mole ratio.

C4 is a high-entropy hydrogen-storage alloy containing vanadium of 1.3 mole ratio.

C5 is a high-entropy hydrogen-storage alloy containing vanadium of 1.7 mole ratio.

C6 is a high-entropy hydrogen-storage alloy containing vanadium of 2.0 mole ratio.

C7 is a high-entropy hydrogen-storage alloy containing vanadium of 2.3 mole ratio.

C8 is a high-entropy hydrogen-storage alloy containing vanadium of 2.6 mole ratio.

C9 is a high-entropy hydrogen-storage alloy containing vanadium of 3.0 mole ratio.

D1 is a high-entropy hydrogen-storage alloy containing manganese of 0 mole ratio.

D2 is a high-entropy hydrogen-storage alloy with manganese of 0.5 mole ratio.

D3 is a high-entropy hydrogen-storage alloy with manganese of 0.75 mole ratio.

D4 is a high-entropy hydrogen-storage alloy with manganese of 1.0 mole ratio.

D5 is a high-entropy hydrogen-storage alloy with manganese of 1.25 mole ratio.

D6 is a high-entropy hydrogen-storage alloy with manganese of 1.5 mole ratio.

D7 is a high-entropy hydrogen-storage alloy with manganese of 2.0 mole ratio.

E1 is a high-entropy hydrogen-storage alloy containing cobalt with a mole ratio equal to 0.

E2 is a high-entropy hydrogen-storage alloy containing cobalt with a mole ratio equal to 0.5.

E3 is a high-entropy hydrogen-storage alloy containing cobalt with a mole ratio equal to 0.75.

E4 is a high-entropy hydrogen-storage alloy containing cobalt with a mole ratio equal to 1.0.

E5 is a high-entropy hydrogen-storage alloy containing cobalt with a mole ratio equal to 1.25.

E6 is a high-entropy hydrogen-storage alloy containing cobalt with a mole ratio equal to 1.5.

E7 is a high-entropy hydrogen-storage alloy containing cobalt with a mole ratio equal to 2.0.

F1 is a high-entropy hydrogen-storage alloy containing iron with a mole ratio equal to 0.5.

F2 is a high-entropy hydrogen-storage alloy containing iron with a mole ratio equal to 1.0.

F3 is a high-entropy hydrogen-storage alloy containing iron with a mole ratio equal to 1.25.

F4 is a high-entropy hydrogen-storage alloy containing iron with a mole ratio equal to 1.5.

F5 is a high-entropy hydrogen-storage alloy containing iron with a mole ratio equal to 2.0.

F6 is a high-entropy hydrogen-storage alloy containing iron with a mole ratio equal to 2.5.

DETAILED DESCRIPTION OF THE INVENTION

The technical characteristics and preparation method of the hydrogen-storage alloy of the present invention will become apparent with the detailed description of preferred embodiments and the illustration of related drawings as follows.

The hydrogen-storage alloy of the present invention has a molecular formula of Co_(u)Fe_(v)Mn_(w)Ti_(x)V_(y)Zr_(z), wherein 0.5≦u≦2.0, 0.5≦v≦2.5, 0.5≦w≦2.0, 0.5≦x≦2.5, 0.4≦y≦3.0 and 0.4≦z≦3.0.

The first embodiment is provided to illustrate a common method of preparing the hydrogen storage alloy of the present invention, and an equivalent preparation method such as a mechanical-alloying method can be used.

The hydrogen storage alloy of the present invention is cast by melting pure metal lumps by a vacuum arc remelter (VAR) to produce the alloy, wherein each pure metal is placed on a water-cooled copper crucible, and then a vacuum pump is turned on until the pressure reaches 2×10⁻² torr, and a valve of the pump is shut, and argon gas is pumped in repeatedly to maintain the pressure at 200 ton, so as to assure a sufficiently low pressure of oxygen in the furnace, such that only the argon gas with a pressure lower than 1 atmosphere can be passed through and ignited by an electric arc, and the metal is melted to a molten form, and after the electric arc stirs the molten metal uniformly, the power is turned off, and the alloy is turned upside down. The aforementioned melting process is repeated for several times, and the alloy is cooled completely and is taken out.

The second embodiment is provided to show the effect of different titanium (Ti) contents.

With reference to FIG. 1 for the effect of specified metals of different mole ratios on the properties of a hydrogen-storage alloy, a specific metal content is adjusted while other metal contents are fixed. For example, the hydrogen storage alloy of the second embodiment has a molecular formula of Co_(u)Fe_(v)Mn_(w)Ti_(x)V_(y)Zr_(z) wherein u, v, w, y and z are fixed to 1, and the value x of (CoFeMnTi_(x)VZr, 0.5≦x≦2.5) is adjusted, and we can observe the effect of the titanium content on the properties of the hydrogen-storage alloy.

Referred to FIGS. 2A to 4B, the range of changing the titanium content is limited to the condition of 0.5≦x≦2.5, or atomic percentages used for indicating the contents of the hydrogen-storage alloy, wherein the Ti content falls within a range from 9.0 to 33.3 and the remaining contents fall within a range from 13.3 to 18.2, and then crystal structure, hydrogen absorption kinetics and hydrogen absorption/desorption capacities are tested, and Designations A1 to A5 represent mole ratios of 0.5, 1.0, 1.5, 2.0 and 2.5 of titanium in the hydrogen-storage alloy, respectively. In the X-ray diffraction patterns, we can observed that the hydrogen-storage alloy has a C14-Laves phase, and the lattice increases as the titanium content increases, and the peaks shift to the right, since the atomic diameter of titanium is greater than the average atomic diameter of other metals in the alloy. At different temperatures (25° C. and 80° C.), the required time (t_(0.9)) will increase with the titanium content of the hydrogen-storage alloy when 90% of the maximum hydrogen absorption capacity is reached, and become smaller gradually, and then become greater gradually. At a lower temperature (25° C.), it takes a longer time to reach t_(0.9). In the analysis of pressure-composition-isotherm (PCI) curve, we can observe that if the titanium content increases at 25° C. and 80° C., the hydrogen affinity is improved, so that the ratio of percentages by weight of all hydrogen atoms to all alloy atoms (H/M value) will be increased, and the maximum ratio of percentages by weight of all hydrogen atoms to all alloy atoms (max H/M value) with the hydrogen storage capacity is 1.8. The maximum (H/M) value at a low temperature is usually greater than the maximum H/M value at high temperature, and this result matches the theory of the hydrogen absorption being a heat releasing reaction. However, if the mole ratio of titanium is 2.5, the H/M value at different temperatures tends to drop, and the maximum H/M value at 80° C. is greater than the maximum H/M value at 25° C. The parameters of a lattice before/after a PCI analysis and the volume expansion ratios of alloys with different titanium contents are listed in Table 1 below.

TABLE 1 Parameters of Lattice Before/After PCI Analysis and Volume Expansion Ratios of Alloys With Different Titanium Contents Parameters of Parameters of Volume Titanium Lattice Before Lattice After PCI Expansion Content PCI Analysis Analysis Ratio (mole ratio) a (Å) c (Å) a (Å) c (Å) (%) 0.5 5.212 8.687 5.273 8.562 0.87 1.0 4.958 8.046 4.982 8.152 2.30 1.5 5.236 8.776 5.303 8.789 2.73 2.0 5.255 8.804 5.413 9.903 19.40 2.5 5.286 8.867 5.522 9.801 20.63

The third embodiment is provided to show the effect of different zirconium (Zr) contents.

With reference to FIG. 1 for the effect of different mole ratios of zirconium on the properties of the hydrogen-storage alloy, the zirconium content is adjusted and the other metal contents are kept constant. In the hydrogen-storage alloy with the molecular formula CoFeMnTiVZr_(z), the zirconium (Zr) content is changed within the range of 0.4≦z≦3.0, or atomic percentages are used for representing the contents of the hydrogen storage alloy, wherein the Zr content falls within the range from 7.5 to 37.5 and the remaining contents fall within the range from 12.5 to 18.5, and crystal structure, hydrogen absorption kinetics and hydrogen absorption/desorption capacity are tested, and the Designations B1 to B9 represent the mole ratios 0.4, 0.7, 1.0, 1.3, 1.7, 2.0, 2.3, 2.6 and 3.0 of zirconium in the hydrogen-storage alloy, respectively. In the X-ray diffraction patterns as shown in FIGS. 5A, 5B, we can observe that the lattice increases with the zirconium content, and thus the (110) peak shifts to the right, and thus both titanium and zirconium have a significant effect to the lattice parameters of the lattice. In FIG. 6, if the zirconium content of the hydrogen-storage alloy is increased, the hydrogen absorption capacity of the hydrogen-storage alloy will be enhanced, and a drop of temperature of the environment of the reaction drops, the hydrogen absorption capacity of the hydrogen-storage alloy will be enhanced, too. In addition, the PCI analysis shows that the volume of lattice will expand 23.83% (as shown in Table 2) if the zirconium content of the hydrogen-storage alloy has a mole ratio equal to 1.6. This result together with the X-ray diffraction patterns can explain a hydrogen-storage alloy with high zirconium content still contains large amount of retained hydrogen, and it shows that the hydrogen-storage alloy has an excellent hydrogen absorption capacity.

TABLE 2 Parameters of Lattice Before/After PCI Analysis and Volume Expansion Ratios of Alloys With Different Zirconium Contents Parameters of Parameters of Volume Zirconium Lattice Before Lattice After PCI Expansion Content PCI Analysis Analysis Ratio (mole ratio) a (Å) c (Å) a (Å) c (Å) (%) 0.4 4.866 7.915 4.866 7.936 0.27 0.7 4.866 7.936 4.935 7.989 3.51 1.0 4.958 8.046 4.982 8.152 2.30 1.3 4.994 8.169 5.273 8.597 17.32 1.6 5.031 8.222 5.342 9.030 23.83 2.0 5.056 8.258 5.383 8.753 20.16 2.3 5.067 8.302 5.411 8.853 21.62 2.6 5.117 8.319 5.469 8.937 22.70 3.9 5.117 8.763 5.469 8.906 16.10

The fourth embodiment is provided to show the effect of different vanadium (V) contents.

With reference to FIGS. 1, 7A, 7B and 8 for the effect of different mole ratios of vanadium on the properties of the hydrogen-storage alloy, the vanadium content is adjusted an the other metal contents are kept constant. In the hydrogen-storage alloy with the molecular formula CoFeMnTiV_(y)Zr, the vanadium (V) content is changed within the range of 0.5≦y≦2.5, or atomic percentages are used for representing the contents of the hydrogen storage alloy, wherein the vanadium content falls within the range from 9.0 to 33.3 and the remaining contents fall within the range from 13.3 to 18.2, and crystal structure, hydrogen absorption kinetics and hydrogen absorption/desorption capacity are tested, and the Designations C1 to B9 represent the mole ratios 0.4, 0.7, 1.0, 1.3, 1.7, 2.0, 2.3, 2.6 and 3.0 of vanadium in the hydrogen-storage alloy respectively. In the X-ray diffraction patterns, we cannot observe any significant shift of each wave peak caused by the hydrogen-storage alloy when the vanadium content is increased, since the atomic diameter of the vanadium metal is smaller than the titanium and zirconium metals and almost equal to the average atomic diameter of the alloy. Therefore, the size of the lattice will not be affected significantly (as shown in Table 3), and the hydrogen absorption capacity of alloys with different vanadium contents will not be affected completely by temperature. However, the enthalpy of formation between vanadium and hydrogen is equal to −37.4 kJ/mol H₂, and thus the alloy with high vanadium content will release hydrogen easily.

TABLE 3 Parameters of Lattice Before/After PCI Analysis and Volume Expansion Ratios of Alloys With Different Vanadium Contents Parameters of Parameters of Volume Vanadium Lattice Before Lattice After PCI Expansion Content PCI Analysis Analysis Ratio (mole ratio) a (Å) c (Å) a (Å) c (Å) (%) 0.4 4.958 8.095 5.006 8.137 2.47 0.7 4.970 8.113 4.982 8.127 0.66 1.0 4.958 8.046 4.982 8.152 2.30 1.3 4.958 8.095 4.994 8.169 2.39 1.6 4.970 8.135 5.006 8.290 3.40 2.0 4.958 8.095 4.982 8.203 2.31 2.3 4.958 8.095 5.043 8.163 4.32 2.6 4.970 8.135 5.043 8.240 4.29 3.9 4.970 8.113 5.043 8.240 4.57

The fifth embodiment is provided to show the effect of different manganese (Mn) contents.

With reference to FIGS. 1, 9A, 9B and 10 for the effect of different mole ratios of manganese on the properties of the hydrogen-storage alloy, the manganese content is adjusted and the other metal contents are kept constant. In the hydrogen-storage alloy with the molecular formula CoFeMn_(w)TiVZr, the manganese (Mn) content is changed within the range of 0.5≦w≦2.0, or atomic percentages are used for representing the contents of the hydrogen-storage alloy, wherein the manganese content falls within the range from 9.0 to 28.6 and the remaining contents fall within the range from 14.3 to 18.2, and crystal structure, hydrogen absorption kinetics and hydrogen absorption/desorption capacity are tested, and the Designations D1 to D7 represent the mole ratios 0, 0.5, 0.75, 1.0, 1.25, 1.5 and 2.0 0 of manganese in the hydrogen-storage alloy respectively. Similarly, in the X-ray diffraction patterns, we cannot observe any significant shift of each diffraction peak caused by the hydrogen-storage alloy when the manganese content is increased, since the atomic diameter of the manganese metal is also smaller. In FIGS. 4A, 4B, the time required to reach 90% of the maximum hydrogen absorption capacity is usually within 100 s, and the maximum hydrogen absorption capacity and the maximum hydrogen desorption capacity of the hydrogen-storage alloy are 1.94 wt % and 1.39 wt %, respectively.

TABLE 4 Properties of Hydrogen-Storage Alloys With Different Manganese Contents at Different Temperatures Maximum Effective Hydrogen Hydrogen Manganese Temper- Absorption Desorption Content ature a c Capacity Capacity t_(0.9) (mole ratio) (K) (Å) (Å) (wt %) (wt %) (s) 0 278 5.02 8.166 1.94 0.48 48 0.5 278 4.976 8.117 1.94 0.88 52 0.75 278 4.953 7.088 1.7 0.88 76 1.0 278 4.972 8.107 1.67 0.92 50 1.25 278 4.937 8.086 1.6 1.09 66 1.5 278 4.907 8.042 1.53 1.22 85 2.0 278 4.922 8.04 0.37 0.37 30 0 298 — — 1.76 0.68 54 0.5 298 — — 1.7 0.78 33 0.75 298 — — 1.63 1.08 42 1.0 298 — — 1.49 1.39 45 1.25 298 — — 1.56 1.39 58 1.5 298 — — 1.32 1.25 96 2.0 298 — — 0.24 0.24 — 0 353 — — 1.54 0.87 57 0.5 353 — — 1.44 1.38 45 0.75 353 — — 1.38 1.38 73 1.0 353 — — 1.18 1.07 45 1.25 353 — — 1.04 1.01 58 1.5 353 — — 0.71 0.67 96 2.0 353 — — 0 0 —

The sixth embodiment is provided to show the effect of different cobalt (Co) contents.

Referred to FIGS. 1, 11A, 11B and 12 for the effect of different mole ratios of cobalt on the properties of the hydrogen-storage alloy, the cobalt content is adjusted and the other metal contents are kept constant. In the hydrogen-storage alloy with the molecular formula Co_(u)FeMnTiVZr, the cobalt (Co) content is changed within the range of 0.5≦w≦2.0, or atomic percentages are used for representing the contents of the hydrogen-storage alloy, wherein the cobalt content falls within the range from 9.0 to 28.6 and the remaining contents fall within the range from 14.3 to 18.2, and crystal structure, hydrogen absorption kinetics and hydrogen absorption/desorption capacity are tested, and the Designations E1 to E7 represent the mole ratios 0, 0.5, 0.75, 1.0, 1.25, 1.5 and 2.0 0 of cobalt in the hydrogen-storage alloy respectively. Similarly, in the X-ray diffraction patterns, we cannot observe any significant shift of each diffraction peak caused by the hydrogen-storage alloy when the cobalt content is increased, since the atomic diameter of the cobalt is also smaller. In FIG. 5, the time required to reach 90% of the maximum hydrogen absorption capacity has a significant difference caused by the cobalt content, and thus the cobalt content of the hydrogen storage alloy will affect the hydrogen absorption efficiency, and the maximum hydrogen absorption capacity and the maximum hydrogen desorption capacity of the hydrogen-storage alloy are 1.91 wt % and 1.39 wt %, respectively.

TABLE 5 Properties of Hydrogen-Storage Alloys With Different Cobalt Contents at Different Temperatures Maximum Effective Cobalt Hydrogen Hydrogen Content Temper- Absorption Desorption (mole ature a c Capacity Capacity t_(0.9) ratio) (K) (Å) (Å) (wt %) (wt %) (s) 0 278 5.04 8.23 2.01 0.51 22 0.5 278 4.987 8.123 1.91 0.54 36 0.75 278 4.976 8.118 1.91 0.71 38 1.0 278 4.972 8.107 1.67 0.92 50 1.25 278 4.944 8.044 1.29 1.22 242 1.5 278 4.917 8.006 0.64 0.56 163 2.0 278 4.902 7.978 0 0 — 0 298 — — 1.83 0.37 21 0.5 298 — — 1.86 0.64 20 0.75 298 — — 1.76 0.85 32 1.0 298 — — 1.49 1.39 45 1.25 298 — — 1.25 1.22 182 1.5 298 — — 0.45 0.41 410 2.0 298 — — 0 0 — 0 353 — — 1.75 0.54 20 0.5 353 — — 1.61 1.07 32 0.75 353 — — 1.54 1.28 50 1.0 353 — — 1.18 1.07 73 1.25 353 — — 0.6 0.57 382 1.5 353 — — 0 0 — 2.0 353 — — 0 0 —

The seventh embodiment 7 is provided to show the effect of different iron (Fe) contents.

With reference to FIGS. 1, 13A, 13B and 14 for the effect of different mole ratios of iron on the properties of the hydrogen-storage alloy, the iron content is adjusted and the other metal contents are kept constant. In the hydrogen-storage alloy with the molecular formula CoFe_(v)MnTiVZr, the iron (Fe) content is changed within the range of 0.5≦w≦2.5, or atomic percentages are used for representing the contents of the hydrogen-storage alloy, wherein the iron content falls within the range from 9.0 to 33.3 and the remaining contents fall within the range from 13.3 to 18.2, and crystal structure, hydrogen absorption kinetics and hydrogen absorption/desorption capacity are tested, and the Designations F1 to F7 represent the mole ratios 0.5, 1.0, 1.25, 1.5, 2.0 and 2.5 of iron in the hydrogen storage alloy, respectively. Similarly, in the X-ray diffraction patterns, we cannot observe any significant shift of each intensity peak caused by the hydrogen-storage alloy when the iron content is increased, since the atomic diameter of the iron metal is also smaller.

In FIG. 6, the time required to reach 90% of the maximum hydrogen absorption capacity may be affected at ambient temperature by the iron content of the hydrogen-storage alloy easily. Changing the iron content can achieve 1.97 wt % and 1.39 wt % for the maximum hydrogen absorption capacity and the maximum hydrogen desorption capacity of the hydrogen-storage alloy, respectively.

TABLE 6 Properties of Hydrogen-Storage Alloys With Different Iron Contents at Different Temperatures Maximum Effective Iron Hydrogen Hydrogen Content Temper- Absorption Desorption (mole ature a c Capacity Capacity t_(0.9) ratio) (K) (Å) (Å) (wt %) (wt %) (s) 0 278 — — 1.97 0.34 28 0.5 278 — — 1.67 0.92 50 0.75 278 5.036 8.205 1.86 0.41 24 1.0 278 4.988 8.155 1.29 0.2 250 1.25 278 4.972 8.107 1.49 1.39 45 1.5 278 4.92 8.022 0.61 0.47 2500 2.0 278 4.914 8.061 0.14 0.1 — 0 353 — — 1.68 0.64 32 0.5 353 — — 1.07 0.24 40 0.75 353 — — 1.49 1.39 73 1.0 353 — — 1.11 0.81 50 1.25 353 — — 0.37 0.34 — 1.5 353 — — 1.97 0.34 28 2.0 353 — — 1.67 0.92 50

In summation of the description above, the content of each metal in the hydrogen-storage alloy of the present invention is adjusted to achieve the hydrogen-storage alloy, such that the hydrogen has excellent hydrogen absorption/desorption and hydrogen-storage capacities in an operation environment at ambient temperature and pressure, and the hydrogen-storage alloy has the potential to become a green energy source.

Many changes and modifications in the above-described embodiment of the invention can, of course, be carried out without departing from the scope thereof Accordingly, to promote the progress in science and the useful arts, the invention is disclosed and is intended to limit only by the scope of the appended claims. 

What is claimed is:
 1. A hydrogen-storage alloy, having a molecular formula of Co_(u)Fe_(v)Mn_(w)Ti_(x)V_(y)Zr_(z), wherein 0.5≦u≦2.0, 0.5≦v≦2.5, 0.5≦w≦2.0, 0.5≦x≦2.5, 0.4≦y≦3.0 and 0.4≦z≦3.0, and atomic percentages used for representing contents of the hydrogen-storage alloy indicating that the content of Co falls within the range from 9.0 to 28.6, and the remaining contents fall within the range from 14.3 to 18.2; or the content of Fe falls within the range from 9.0 to 33.3 and the remaining contents fall within the range from 13.3 to 18.2; or the content of Mn falls within the range from 9.0 to 28.6, and the remaining contents fall within the range from 14.3 to 18.2; or the content of Ti falls within the range from 9.0 to 33.3, and the remaining contents fall within the range from 13.3 to 18.2; or the content of V falls within the range from 9.0 to 33.3 and the remaining contents fall within the range from 13.3 to 18.2; or the content of Zr falls within the range from 7.5 to 37.5, and the remaining contents fall within the range from 12.5 to 18.5.
 2. The hydrogen-storage alloy of claim 1, wherein the hydrogen storage alloy is in a C14-Laves phase. 